Eliezer—your argument is logically invalid. (5) does not follow from (3) and (4) as stated. Note that the epiphenomenalist has a theory of reference/mental content according to which my thoughts about consciousness are partly constituted by the phenomenal properties themselves. That is, the qualia are part of “that-which-makes-me-think-I-have inward awareness”. Otherwise, I wouldn’t be having thoughts about consciousness at all. (Zombies don’t. They merely have brain states, which are not ‘about’ anything.) So I can grant that ‘consciousness’ refers to (part of) “that-which-makes-me-think-I-have” it, without it following that the object of reference (viz. phenomenal properties) are also present in the zombie world.
You can save the logical validity of the argument by tidying up (4), so that you instead assert that ‘consciousness’ must refer to the cause of my verbalization, or perhaps of the underlying brain state—build in some limitation to ensure that it’s some feature shared by any physical duplicate of myself. But then it’s a false premise, or at least question-begging—no epiphenomenalist is going to find it remotely plausible. And since we can offer a perfectly consistent alternative theory of reference, we are not committed to any logical inconsistency after all.
Jed Harris—you’re just reiterating old-fashioned radical skepticism. I might be deceived by an evil demon, or be a Brain in a Vat, or be deceived by alternative bridging laws into having the exact same experiences even if the physical world were very different from how I take it to be. Bleh. It’s a fun puzzle to think about, but it’s not a serious problem. Any adequate epistemological theory will explain how it’s possible for us to have knowledge despite the logical possibility of such scenarios.
Hal—our qualia are determined by physical states (+ the bridging laws), so no, we wouldn’t “feel chagrin” etc. (You seem to be assuming some kind of intuitive substance-dualist picture, where the soul does its thinking independently of its physical substrate. That’s not property dualism.)
Caledonian—why do you keep asking questions I’ve already answered? Once again, just follow my above link.
P.S. There seems to be a lot of confusion around about the targets of epistemic assessment, and what “rational brains” would conclude about the relative likelihood that they’re zombies, etc. I think this rests on some pretty fundamental philosophical errors, so will write up a new post on my blog explaining why.
Eliezer—your argument is logically invalid. (5) does not follow from (3) and (4) as stated. Note that the epiphenomenalist has a theory of reference/mental content according to which my thoughts about consciousness are partly constituted by the phenomenal properties themselves. That is, the qualia are part of “that-which-makes-me-think-I-have inward awareness”. Otherwise, I wouldn’t be having thoughts about consciousness at all. (Zombies don’t. They merely have brain states, which are not ‘about’ anything.) So I can grant that ‘consciousness’ refers to (part of) “that-which-makes-me-think-I-have” it, without it following that the object of reference (viz. phenomenal properties) are also present in the zombie world.
You can save the logical validity of the argument by tidying up (4), so that you instead assert that ‘consciousness’ must refer to the cause of my verbalization, or perhaps of the underlying brain state—build in some limitation to ensure that it’s some feature shared by any physical duplicate of myself. But then it’s a false premise, or at least question-begging—no epiphenomenalist is going to find it remotely plausible. And since we can offer a perfectly consistent alternative theory of reference, we are not committed to any logical inconsistency after all.
Jed Harris—you’re just reiterating old-fashioned radical skepticism. I might be deceived by an evil demon, or be a Brain in a Vat, or be deceived by alternative bridging laws into having the exact same experiences even if the physical world were very different from how I take it to be. Bleh. It’s a fun puzzle to think about, but it’s not a serious problem. Any adequate epistemological theory will explain how it’s possible for us to have knowledge despite the logical possibility of such scenarios.
Hal—our qualia are determined by physical states (+ the bridging laws), so no, we wouldn’t “feel chagrin” etc. (You seem to be assuming some kind of intuitive substance-dualist picture, where the soul does its thinking independently of its physical substrate. That’s not property dualism.)
Caledonian—why do you keep asking questions I’ve already answered? Once again, just follow my above link.
P.S. There seems to be a lot of confusion around about the targets of epistemic assessment, and what “rational brains” would conclude about the relative likelihood that they’re zombies, etc. I think this rests on some pretty fundamental philosophical errors, so will write up a new post on my blog explaining why.